The present invention relates generally to a drum brake shoe assembly and, in particular, to a drum brake shoe assembly having an improved brake shoe support structure to retain the drum brake shoe in position relative to a backing plate.
Conventional drum brakes include a pair of drum brake shoes each having a semicircular rim with a radially outer surface and a band of friction material attached thereto. A strengthening web is attached to the rim and extends radially inwardly along most of the length of each shoe. The brake shoes are mounted on a backing plate of the drum brake assembly and supported in place by a hold down mechanism. A conventional hold down mechanism consists of a hold down pin having a first end connected to the backing plate and a second end extending through a hole in the brake shoe web. A coil spring is typically disposed between the second end and the web to urge the brake shoe toward the backing plate. While most drum brake assemblies use one hold down mechanism per shoe, it is known to use two hold down mechanisms for each brake shoe, as disclosed in U.S. Pat. No. 5,201,390 to Anderson et al. However, using two hold down mechanisms per brake shoe is generally undesirable due to the increased cost and complexity.
To brake the vehicle, the brake shoes are moved radially outwards by an actuator, such as a hydraulically or pneumatically actuated brake cylinder, until the friction material contacts a corresponding friction surface on the brake drum. The friction created during contact slows the rotation of the drum and wheel, thus slowing the vehicle.
However, the applicant has discovered that the conventional brake shoe support configuration using only one hold down mechanism per shoe allows considerable unwanted shoe movement in the lateral direction (also known as the axial direction in relation to the brake drum or wheel) during braking in response to variations in the surface of the brake drum. The applicant has further discovered that the movement of the shoe in the lateral direction allows the shoe to impact with the backing plate causing unacceptable noise during braking. It is desirable to reduce the braking noise by reducing the unwanted shoe movement during braking while keeping the added cost and complexity to a minimum.